The invention lies in the electronics field. Specifically, the present invention concerns a multiple preliminary stage circuit for a television tuner with at least a first band having an amplification stage and a second band having an amplification stage.
Television signals transmitted over a frequency range between about 50 and 850 MHz are generally processed in three bands of a television tuner namely UHF band, a VHF-HF1 band and a VHF2 band. However, it is also possible to combine the VHF1 band and the VHF2 band into a single VHF band so that the most cost-effective tuner concepts have a total of two bands.
A circuit configuration for range switching in tuners is known from U.S. Pat. No. 5,204,645 to Hohmann (European patent application EP-A-0 457 932). There, a MOS tetrode is used as an amplifier. The source terminals of the MOS tetrode are switchable via a control circuit between the two supply potentials 0 V and 5 V. Depending on the applied potential, the desired range is selected.
A two-band television tuner is shown in FIG. 5 as an example.
The television tuner depicted in FIG. 5 comprises a UHF band 1 and a VHF band 2. Depending on the frequency of the desired television signal, either the UHF or VHF band is activated (band switching). A television signal supplied via an antenna 3 is fed in band 1 or 2 initially to a preselection circuit 4 or 5 for crude adjustment. A controllable amplifier stage 6 and 7 is connected after these preselection circuits 4 and 5, in which the television signals are amplified as a function of the signal level. These amplification stages are implemented with dual gate MOS-FETs. These field-effect transistors can be readily adjusted to resonance circuits. They are described, for example, in the above-mentioned U.S. Pat. No. 5,204,645.
Band pass filters 8 and 9, at whose output a tuner-IC 10 converts the selected channel to the television line frequency with oscillators 11, 12, are connected after the amplifier stages 6 and 7.
Amplification control signals are fed to the two amplifier stages 6 and 7, which is shown by arrows 13 and are engaged in alternation with tuner-IC via a switching logic 30. These functions require significant discrete component expense.
It is accordingly an object of the invention to provide a two-band preliminary stage circuit for television tuners, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which is further simplified so that it can be designed more compact and get by with fewer components.
With the foregoing and other objects in view there is provided, in accordance with the invention, a multiple preliminary stage circuit for a television tuner, comprising:
a first band with a first band amplifier stage having a transistor and a second band with a second band amplifier stage having a transistor;
a common chip common to the first band and the second band and having integrated therein the first band amplifier stage and the second band amplifier stage;
the common chip having a terminal for receiving a band switching signal and a terminal for receiving an amplification control signal;
a tuner-IC connected to the common chip for switching, with a single band switching signal, the first and second amplifier stages;
a reference transistor connected to a respective transistor of a respective the amplifier stage to form a current mirror circuit; and
a further transistor having a controlled section connected between the reference transistor and a reference potential for selectively blocking the controlled section of the reference transistor or connecting the controlled section through to the reference potential in dependence on the band switching signal, and wherein the respectively other amplifier stage is selectively activated and deactivated in complementary fashion via the band switching signal.
In other words, the object is satisfied with the integration of the two bands in a common chip, to which a band switching signal and an amplification control signal can be fed.
In the multiple preliminary stage circuit according to the invention the two amplifier stages of the existing two-band preliminary stage circuit are therefore accommodated on one chip so that circuit parts and housing terminals can be jointly utilized for both bands. It should be noted that the amplifier stages of more than two bands can also optionally be integrated in the one chip.
A first stage can then be assigned to the UHF band, whereas the second stage operates in the VHF band.
In accordance with an added feature of the invention, a reference transistor of the respectively other amplifier stage is short-circuited with the reference potential.
In accordance with an additional feature of the invention, the amplifier stages have control inputs shorted to the reference potential.
In accordance with another feature of the invention, the common chip further comprises at least one operating point adjustment circuit and a switching logic.
In accordance with a further feature of the invention, the operating point adjustment circuit comprises a current source, an auxiliary element, and the reference transistor in the current mirror circuit for the corresponding amplifier stage.
The chip therefore contains for each band an MOS-FET amplifier stage, in which all MOS-FET amplifier stages of one chip are switchable by only one band switching signal from a tuner-IC. In addition, the chip has at least one operating point adjustment circuit and a switching logic. The operating point adjustment circuit then consists of a current mirror circuit with a reference transistor lying on the MOS-FET amplifier stage. The band switching signal is fed to the switching logic, whereas the amplification control signal is fed to a second gate of an MOS-FET amplifier stage whose first gate is exposed to an input signal.
In accordance with a concomitant feature of the invention, the common chip is enclosed in an SMD housing (SMD=surface mounted device).
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a multiple preliminary stage circuit for television tuner, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.